I placed a brief comment on the Decadent Indulgence some time ago - but since my wife still absolutely loves this thing I thought it deserved a full review.
Interestingly there are multiple new versions of this classic - and someday I'm going to try them out - probably the waterproof one - because the lack of waterproof features is the Achilles-hell of this classic performer.

Many EF readers seemed focused on materials - this one is TPR which makes it OK to use water, oil or silicone based lubes. Although my wife has had reactions to jelly materials - she have never had any adverse reaction to this one - oh contraire!

The Decadent Indulgence is obviously in the category of rabbit-vibes - but the clitoral vibe is actually in the shape of a humming bird - which is significant because the wings of the humming bird are a great tool for adding labial stimulation to the symphony of other sensations.
My wife has always been clitoral-centric with regard to orgasm - not so unusual - but worth noting. For the first few years we owned this toy she never let me use the rotating shaft - she just liked to 'hold on to it' - the squeeze made orgasm easier than just a clit-vibe alone.
That also tells you something - we've been using this thing for 4-5 years and it's still going strong.

Another important feature of the humming bird is that it sets at the end of a short but flexible stem which allows for easy and precise placement for maximum benefit. Other vibes like the Wild G and Rechargeable Rabbit that we have - the clit-vibe is close-coupled to the shaft making adjustment more difficult or near impossible - so those two find themselves in the also-ran box.

One interesting thing that we encountered is that the very tip - the beak of the humming bird vibrated so strongly that eventually she asked me to trim it off - so we have a beak-less humming bird!

As we have moved on from clit-only vibes to dual-vibes like the Decadent Indulgence - we started to combine some straight up dildos with vibes - she loves glass now. Since getting use to more vigorous internal stimulation - she's now interested in using the rotational shaft of this toy.

The first thing we noticed is that we had to be more careful with batteries - when we just used the clit-vibe - the 4 AAs would last forever - now that we combine the shaft rotations with the clit-vibe - fresh batteries are more important - but I would still rate battery life as excellent.
The insert-able shaft is 5.5" long with three tiers of metal balls - like BBs on tracks positioned from 1.25' to 3" above the base of the clit-vibe or starting about 3" down from the tip. The shaft is a little less than 1.5" in diameter.

Now that my wife is open to - and even occasionally asked for the rotating to be activated - I haven't noticed that the rotating shaft & BBs has brought on any gushing orgasms. But I when she's about to climax the shaft nearly stops rotating - as she squeezes the shaft. You can hear the poor little motor strain to overcome the powerful vice restraining it!

After many years of gratifying orgasms - I can't remember it ever failing to deliver - the only complaint is the battery cover comes off very easily - at the wrong times and clean up is difficult because you have to make sure the water doesn't get near the batteries. I kind wish it would fail so I could justify investing in the Ultimate Decadent Indulgence (waterproof) model!

Still the best! I'm always searching for something a little better. I've purchased 4 other 'rabbit' vibes (none have the proverbial rabbit) - and still none measure up to the original Decadent Indulgence (DI).

For my latest effort I decided to 'stay in the family' of DI products. The choices were:

DI2 which is not waterproof (important in my decision). Other factors were; it keeps the rotating metal balls (good), is smaller in diameter (not so good) and has the rabbit instead of the hummingbird (not so good) - my wife loves the sensations on her vulva from the wings of the little bird

DI3 which is not water proof, (not good), has plastic rotating beads (not good)) and has an elephant with large ears that appear to have the same function as the hummingbird wings(OK?)

Ultimate DI - this one is waterproof (required), keeps the hummingbird (good), is a little larger in diameter (good)and has plastic rotating beads (not so good). So I think 3 out of 4 ain't bad and took the plunge and ordered the Ultimate DI - despite my concern that it only has 3 AAs compared to 4 for the others.

It turns out that the 4th battery is required if you want to run the rotating shaft and strong vibes at the same time!

The end result is that the original DI is still the hands down favorite at our house!